1. Field of the Invention
The present invention relates to a hot press apparatus and, more precisely, it relates to a hot press apparatus which can be advantageously used to form a laminate such as a printed circuit board which requires high precision.
2. Description of the Related Art
For instance, in a known multi-stage hot press apparatus which is used to obtain laminates (multi-layered products), such as printed circuit boards which are generally indicated at 80 in FIG. 5, a plurality of workpieces L, L, L to be multi-layered are placed between heating plates 85, 85, 85 in a chamber 82 on a machine bed 81. A movable plate 86 is moved upward by a ram 88 to sequentially move the heating plates 85 upward in order to heat and press the workpieces L, L, L between the heating plate 85 on which the workpiece L is placed and the upper heating plate in each stage. Note that in the uppermost stage, the workpiece L placed on the uppermost movable heating plate 85 is heated and pressed between the heating plate 85 and the upper stationary heating plate 85U to obtain the laminates (multi-layered products). In FIG. 5, numeral 83 designates the support posts, 84 the guide rails, 85a the stage, 87 the stationary plate, and 89 the thermally insulating plate.
In the apparatus as shown in FIG. 5 in which the movable plate 86 is moved upward by the ram 88, if the number of the heating plates 85 is large (e.g., not less than 15 stages), the height of the apparatus is in the order of several meters, and hence, it is necessary to emplace a cylinder apparatus 88A for the ram 88 in a pit P formed in the floor surface F in order to adjust the height in connection with peripheral conveyor devices, etc., as can be seen in the drawings. However, the pit-type hot press is costly because many constructions or equipments are necessary. Moreover, it is difficult to modify the layout and to enlarge or relocate the apparatus.
To eliminate these drawbacks of the pit type hot press, in recent years, pit-less type hot press apparatuses in which no pit P is necessary have been proposed. As can be seen in FIG. 6 in which a pit-less type hot press is generally indicated at 90, the movable plate 96 is pulled up by the cylinder devices 100 toward the stationary plate 97. In this structure, the height of the apparatus can be shortened by a height corresponding to the ram which is adapted to move the movable plate 96 upward, so that the pit P can be dispensed with. In FIG. 6, numeral 91 designates the machine bed, 92 the chamber, 93 the support posts, 94 the guide rails, 95 the heating plates, 95U the upper stationary heating plate, 95a the stage, 99 the thermally insulating plate, 109 the jack bolts for restricting the downward displacement, and L the workpieces (to be laminated), respectively.
However, the pit-less type hot press has the following drawbacks.
Namely, in order to pull the movable plate 96 up toward the stationary plate 97 by the cylinder devices 100, it is necessary to connect pull shafts 101 of the cylinder devices 100 to the movable plate 96 at the outer peripheral edges 96S thereof, in view of the presence of the heating plates 95, 95 between the stationary plate 97 and the movable plate 96. When the workpieces L are pressed by pulling the movable plate portions 96S upward by the use of the pull shafts 101, the movable plate 96 is deformed into a concave shape at the center portion thereof and the stationary plate 97 is also deformed into a concave shape at the center portion thereof on which the workpieces L are placed, as schematically shown in FIG. 7. Consequently, the workpiece L tends to be deformed into a barrel shape in cross section in which the central portion is slightly bulged outward. This phenomenon is caused by a difference between the pressure applied to the central portion of the workpiece L and the pressure applied to the peripheral edge thereof. The non-uniform pressure leads to a non-uniform thickness of the workpiece L or the production of wrinkles or the presence of air between the layers of the laminate, etc., thus resulting in defective products. Note that, in FIG. 7, only one stage is schematically shown for clarity and the deformation is exaggerated and is actually on the order of a few tenths of a mm.
In particular, for a printed circuit board, through holes or a conductor pattern is formed in or on the hot-pressed laminate (substrate) L and the non-uniform thickness or the production of wrinkles or presence of air, etc., become more serious problems.
It is an object of the present invention to provide a hot press apparatus in which the advantages of the pit-less type hot press are preserved and the pressure can be uniformly applied to a workpiece to prevent the production of wrinkles or the presence of air in the laminate, whereby a high precision laminate product can be obtained.
To achieve the object mentioned above, according to an aspect of the present invention, there is provided a hot press apparatus in which workpieces are placed between heating plates in a chamber of a machine bed, so that the workpieces are heated and pressed by moving a movable plate toward a stationary plate to form a laminate, wherein the movable plate is held at its peripheral portions by shaft members and is moved toward the stationary plate by a drive means, and provision is made of a center portion pressing member at the center portion of the movable plate to press the substantially center portions of the heating plates.
Preferably, the center portion pressing member is provided with a pressing surface which covers the entirety or substantially entirety of the workpieces placed on the heating plates.